Abstract
Probiotics are considered ecofriendly alternatives to antibiotics as immunostimulants against pathogen infections in aquaculture. In the present study, protease-, amylase-, cellulase-, and xylanase-producing Bacillus safensis NPUST1 were isolated from the gut of Nile tilapia, and the beneficial effects of B. safensis NPUST1 on growth, innate immunity, disease resistance and gut microbiota in Nile tilapia were evaluated by feeding tilapia a basal diet or basal diet containing 105 and 106–107 CFU/g for 8 weeks. The results showed that the weight gain, feed efficiency and specific growth rate were significantly increased in tilapia fed a diet containing 106 CFU/g and 107 CFU/g B. safensis NPUST1. Intestinal digestive enzymes, including protease, amylase and lipase, and hepatic mRNA expression of glucose metabolism and growth-related genes, such as GK, G6Pase, GHR and IGF-1, were also significantly increased in the 106 CFU/g and 107 CFU/g B. safensis NPUST1 treated groups. Immune parameters such as phagocytic activity, respiratory burst and superoxide dismutase activity in head kidney leukocytes, serum lysozyme, and the mRNA expression of IL-1β, IL-8, TNF-α and lysozyme genes were significantly induced in the head kidney and spleen of 106 CFU/g and 107 CFU/g B. safensis NPUST1 treated fish. The cumulative survival rate was significantly increased in fish fed a diet containing 106 CFU/g and 107 CFU/g B. safensis NPUST1 after challenge with Streptococcus iniae. Dietary supplementation with B. safensis NPUST1 improves the gut microbiota of Nile tilapia, which increases the abundance of potential probiotics and reduces the abundance of pathogenic pathogens. The present study is the first to report the use of B. safensis as a potential probiotic in aquaculture, and a diet containing 106 CFU/g B. safensis NPUST1 is adequate for providing beneficial effects on growth performance and health status in tilapia.
Highlights
A variety of Bacillus species have been used as probiotics in diverse fish species, a high proportion of Bacillus are derived from the non-natural habitats of the host, and only a few studies have involved extracellular digestive enzyme-producing Bacillus
Studies have reported that supplementation of hydrolytic enzymes such as cellulase and xylanase in feed can efficiently solve nonstarch polysaccharide (NSP) problems in aquaculture [31,32]; the high cost of enzymes supplemented in feed is difficult to manage in aquaculture
Reports have shown that dietary supplementation with hydrolytic enzymes-producing probiotics could obviously enhance feed efficiency (FE) and growth performance in white shrimp (Litopenaeus vannamei), zebrafish (Danio rerio), pla-mong (Pangasius bocourti), golden pompano (Trachinotus ovatus), and Nile tilapia [17,18,33,34,35,36]
Summary
Global aquaculture has been considered the fastest growing method for producing animal protein to satisfy the increasing global food demand. According to Food and Agriculture Organization (FAO) 2020 statistics, aquaculture accounts for more than. 50% of the total fish produced for human consumption [1]. Nile tilapia (Oreochromis niloticus) is one of the most popular fish species worldwide due to its properties including fast growth, high tolerance to environmental stress and high marketability. Tilapia has been farmed in over 100 countries worldwide and is an important source of income in several developing countries. Intensive culture is commonly used in tilapia aquaculture to achieve high production yields in places with limited farmland. The high incidence of Microorganisms 2021, 9, 2494.
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